Costs of skin and skin structure infections due to Staphylococcus aureus: an analysis of managed-care claims

Objectives: The incidence of skin and skin structure infections (SSSIs) due to Staphylococcus aureus (SA) is increasing. The objective of this study was to assess the costs of a treatment episode for SA-SSSIs. Methods: This retrospective analysis used a managed-care claims database to assess the duration and costs of incident SA-SSSI episodes treated with selected antibiotics (IV vancomycin, oral linezolid, and daptomycin, termed 'study antibiotics'). Patients were included if they had an ICD-9-CM diagnosis of an SSSI and SA between January 1, 2002 and December 31, 2005. Treatment episodes began on the date of the first antibiotic and ended when the patient had fourteen consecutive days without a study antibiotic or SSSI hospitalization. Costs, represented by health plan payments for SSSIs and overall, were updated to 2005 US dollars. A generalized linear model (GLM) assessed predictors of costs. Results: A total of 1997 patients met the selection criteria. Mean (+/- SD) age was 46.3 (+/- 12.6) years and 55.9% of patients were male. Average episode length was 24 days, and over 95% of patients received IV vancomycin or oral linezolid as their initial study antibiotic. Patients remained on study antibiotics for an average of 16.4 days, and only 5% of patients were switched to another study antibiotic. Mean (+/- SD) overall episode costs were $8865 (+/- $20 003), primarily composed of inpatient and outpatient medical services. Treatment failure (i.e., study antibiotic switching or hospitalization), younger age, a diagnosis of bacteremia, osteomyelitis, or multiple complications during the episode, treatment with daptomycin, and greater Charlson co-morbidity score were significant positive predictors of overall costs. Alternatively, treatment with oral linezolid and hospitalization before the start of the outpatient treatment episode were significant negative predictors of overall costs. Mean (+/- SD) SSSI-related costs were $4551 (+/- $11 058). Limitations: Medical charts and laboratory test results were not available to confirm SSSI and SA diagnoses, and no information was available regarding antibiotics received in the inpatient setting. Conclusions: The costs of treating SA-SSSIs are substantial and vary by failure rates, co-morbidities, and type of antibiotic therapy.